Field of the Invention
Embodiments of the present invention relate generally to a charged particle beam writing apparatus and a charged particle beam writing method, and more specifically, relate to a writing apparatus and method that perform proximity effect correction in the case, for example, where a dose is modulated (or adjusted) due to a prescribed effect other than the proximity effect.
Description of Related Art
The lithography technique that advances miniaturization of semiconductor devices is extremely important as a unique process whereby patterns are formed in semiconductor manufacturing. In recent years, with high integration of LSI, the line width (critical dimension) required for semiconductor device circuits is decreasing year by year. For forming a desired circuit pattern on such semiconductor devices, a master or “original” pattern (also called a mask or a reticle) of high accuracy is needed. Thus, the electron beam (EB) writing technique, which intrinsically has excellent resolution, is used for producing such a high-precision master pattern.
For example, a writing apparatus using a single beam is known, and further, there can be cited a writing apparatus employing the raster method. In the writing apparatus employing the raster method, for example, an electron beam emitted from the electron gun passes through a mask with one hole to be shaped, and the shaped beam is deflected by a deflector to move in a tracing manner on the target object or “sample” in order to irradiate a necessary point by blanking control.
Further, for example, a writing apparatus using multiple beams is known. When compared to the case of writing or “drawing” a pattern with a single electron beam, since it is possible to irradiate many beams at a time in multi-beam writing, the throughput can be greatly increased. For example, in the writing apparatus employing the multi-beam system, multi-beams are formed by letting portions of an electron beam emitted from an electron gun pass through a corresponding hole of a plurality of holes in the mask, and each beam is blanking-controlled such that each unblocked beam is reduced by an optical system and deflected by a deflector so as to irradiate a desired position on the target object.
Moreover, besides the writing apparatus employing the raster method described above, as the writing apparatus using a single beam, there can be cited, for example, a variable-shaped beam (VSB) writing apparatus. In the writing apparatus of the VSB system, while forming a shot beam by a blanking control, the relative position of two-stage shaping apertures through which the beam passes is variably controlled, thereby variably shaping a beam of each shot. Then, the variably shaped beam is deflected by a deflector so as to irradiate a desired position on the target object.
In the various writing systems described above, there is a problem with respect to writing by the raster method or writing method with the multi-beam system in that, when a pattern edge or corner is written, if the pattern edge (boundary) is deviated from the pixel boundary, a desired shape of the pattern edge or corner cannot be formed with a design irradiation dose thereon. Accordingly, it has been examined to perform correction by adjusting the dose thereto.
With recent development of the optical lithography technology and shorter wavelengths due to EUV (extreme ultraviolet), the number of electron beam shots required for mask writing is increasing acceleratingly. On the other hand, for ensuring the line width accuracy needed for micropatterning, it is aimed to diminish shot noise and pattern edge roughness by making resist less sensitive and increasing the dose. Thus, since the number of shots and the amount of dose increase limitlessly, the pattern writing time also increases limitlessly. Therefore, in the writing apparatuses of various writing systems described above, it is now examined to reduce the writing time by increasing the current density.
However, if the target is irradiated with an increased amount of energy as a higher density electron beam in a short time, another problem occurs in that the substrate overheats resulting in a phenomenon called “resist heating” of changing the resist sensitivity and degrading the line width accuracy. To solve this problem, it is suggested to calculate, for each minimum deflection region in the deflection region, a representative temperature of the minimum deflection region concerned based on heat transfer from other minimum deflection regions written prior to the current one, and to modulate the dose by using the representative temperature (refer to Japanese Patent Application Laid-open (JP-A) No. 2012-069675).
On the other hand, in the electron beam writing, a phenomenon called a “proximity effect” occurs when electron beams irradiate a mask covered with resist to write a circuit pattern thereon. The proximity effect occurs by backscattering of electron beams penetrating the resist film, reaching the layer thereunder to be reflected, and entering the resist film again. As a result, a dimensional variation occurs, that is, a written pattern is deviated from a desired dimension. In order to avoid this phenomenon, a proximity effect correction operation that suppresses such dimensional variation by, for example, modulating the dose is performed in the writing apparatus.
However, even when the dose is adjusted by performing proximity effect correction calculation, if subsequently performing dose modulation for correcting various effects other than the proximity effect, such as pattern edge/corner correction, resist heating correction described above, etc., there arises another problem in that correction residual error occurs regarding proximity effect correction.
As described above, since correction residual error arises in proximity effect correction, it is necessary to again perform proximity effect correction calculation after dose modulation calculation for correcting various effects. However, even in such a case, there is still a problem in that since the calculation amount of proximity effect correction is large, rather sufficient computer resource and processing time are needed, thereby resulting in a problem of difficulty of real time correction calculation. Accordingly, it is necessary to efficiently perform the processing.